This invention relates to liquid distribution systems used for irrigation and like purposes.
Large scale irrigation systems for golf courses, cemeteries and the like spread out over a vast area. For example, a sprinkler head in one piping path in the system can be a mile or more away from another sprinkler head in another piping path in the system.
In the past, electrical control systems have been developed for controlling the overall operation of such large scale irrigation systems. In such an electrically controlled irrigation system, there are a plurality of piping paths each including its own electrically actuated remote control valve. A central sequencing control station programs the operation of the system by sequentially providing to each remote control valve, during a timed interval, a command voltage. The amount of electrical wiring needed to interconnect the central station and the various remote control valves is considerable. The material cost and the labor expenses incident to laying this wiring over stretches of a mile or more is a significant factor in the cost of the system.
Such complex systems are inevitably prone to a variety of types of faults, particularly because most of the system is outdoors and exposed to a variety of contaminants. For example, sprinkler heads are sometimes clogged by insects or other debris. Occasionally, cracks develop in the piping paths downstream of the remote control valves and thus flooding ensues adjacent the cracks when the remote control valve is held open. The remote control valves themselves are failure-prone. Sometimes, they stick closed notwithstanding the receipt of actuation current. This results in a lack of proper irrigation when the failure goes unnoticed. And, because of the large distances involved, operating personnel at the central station frequently will not be within viewing distance of the area where the fault occurs. On the other hand, sometimes the valves stick open notwithstanding the termination of actuating current. This leads to excess watering of the area where this fault occurs.
Owing to the above-mentioned cost factors relating to the wiring, it is undesirable to lay separate wires between the central station and the various remote valves for purposes of carrying fault-indication signals.